(a) Field of the Invention
The present invention relates generally to a three-dimensional image display system and method thereof. More particularly, the present invention relates to a three-dimensional image display system and method based on integral photography (IP).
(b) Description of the Related Art
Among the technologies that display three-dimensional images, IP (Integral Photography), which uses a lens array, was first proposed by Lippmann in 1908. However, IP did not attract much attention at that time due to limitations of image capturing and displaying devices. But it has recently begun to be studied extensively with the development of high resolution image capturing and displaying devices.
FIG. 1(a) shows the basic principles of conventional IP.
As shown in FIG. 1(a), the system for realizing IP comprises two functional parts: a pickup and a display. The pickup comprises a lens array which forms elemental images of three-dimensional objects, and a capturing device which captures the elemental images formed by the lens array. The display comprises a displaying device which displays the elemental images that are taken by the capturing device, and a lens array which reproduces the elemental images into three-dimensional images. Each lens array comprises a plurality of elemental lenses.
In the pickup, many perspectives of the three-dimensional object observed from various directions, which are referred to as elemental images, are formed by the elemental lenses that constitute the lens array. These elemental images are captured and stored by the image capturing device. In the display, the reverse process of the pickup is performed. That is, the elemental images that were stored by the image capturing device are displayed by the image displaying device. These elemental images are integrated through the lens array to form three-dimensional images (also referred to as integrated images) with each perspective at the original positions.
CGIP (Computer-Generated Integral Photography), which produces elemental images by computer graphics, has been proposed to overcome a pseudoscopic phenomenon of the integrated images and to simplify the system structure.
FIG. 1(b) shows the configuration of the CGIP system. As shown in FIG. 1(b), the elemental images of the three-dimensional object are generated by computer graphics and then transmitted to the displaying device (LCD panel) to reproduce the three-dimensional image by the lens array. The position where the three-dimensional image (integrated image) is formed varies with the distance between the lens array and the display panel. The above-noted relation is described by the subsequent equation.1/d+1/g=1/f  [EQUATION 1](where d is the distance between the integrated image and the lens array, g is the distance between the lens array and the LCD panel, and f is the focal length of the each elemental lens which comprises the lens array.)
Namely, when the distance between the lens array and the LCD panel is longer than the focal length of the elemental lens, the position of the image has a positive value, representing that the integrated image is formed in front of the lens array as a real image (a real IP). In another case, when the distance between the lens array and the LCD panel is shorter than the focal length of the elemental lens, the position of the image has a negative value, representing that the integrated image is formed behind the lens array as a virtual image (a virtual IP).
FIG. 2 shows the difference between real IP and virtual IP. In virtual IP, since the position of the integrated image is further from the observer compared to the real IP case, the observer may advantageously see the three-dimensional image at a nearer position from the lens array and the LCD panel than the real IP. As shown in FIG. 2, an implementation of the virtual IP is similar to that of the real IP except that the elemental images of the virtual IP are erect images while those of the real IP are reverse images.
One of the problems of the IP system is a limitation of the viewing angle. In the IP system, an elemental image which exceeds the region of the corresponding elemental lens is removed from the displaying device to prevent the image overlapping phenomenon in which repeated integrated images in addition to the original integrated image are observed simultaneously. This process essentially limits the viewing angle of the IP system. Accordingly, the viewing angle thus limited is expressed in EQUATION 2.
                    θ        =                  2          ⁢                      arctan            ⁡                          (                              ψ                                  2                  ⁢                  g                                            )                                                          [                  EQUATION          ⁢                                          ⁢          2                ]            (where θ is the viewing angle of the system, Ψ is the pitch of the elemental lens, and g is the distance between the lens array and the displaying device.)
As expressed in EQUATION 2, since the viewing angle is proportional to the pitch of the elemental lens and inversely proportional to the distance between the lens array and the displaying device, it is required to either narrow the distance between the lens array and the displaying device or widen the pitch of the elemental lens, so as to widen the viewing angle. However, the distance between the lens array and the displaying device may not be arbitrarily reduced by more than a predetermined value, because the resolution of the integrated image degrades as the distance between the lens array and the displaying device decreases. In addition, widening of the pitch of the elemental lens to a great extent problematically causes the available depth of the integrated image to be decreased.
It is preferably required for a group of people to be able to view the reproduced three-dimensional images with a wide viewing angle, but the above-described limited viewing angle of the IP system fails to reach the desired realization of wide views, and this has been indicted as a weak point.